A communication network includes network elements that route packets through the network, predominantly in line card hardware. To route packets, network elements often utilize intermediate system to intermediate system (ISIS) protocol. In certain cases, multiple ISIS instances will be instantiated on a network element, to allow for parallel processing, routing and redundancy.
Individual network elements may be identified by a terminal identifier (TID). TID Address Resolution Protocol (TARP) is commonly used to map such TIDs to a Network Service Access Point (NSAP) address associated with an ISIS instance. However, a network element may be configured with such that TARP supports the mapping of a TID to one NSAP address, regardless of the number of ISIS instances present on such a network element. Accordingly, when performing a mapping on a multiple ISIS instance network element, the TID may be mapped to only one of the multiple NSAP addresses. Thus, to other network elements, a multiple ISIS instance network element appears as a single ISIS instance network element.
Accordingly, a TID to NSAP address mapping for a multiple ISIS instance network element may become stale when a link failure, other network failure or link disconnection occurs due to the fact that a single TID is shared among the multiple ISIS instances. When such a disconnection occurs and a TID is mapped to the NSAP address of the network element reachable via the failed link, all traffic to the network element may be dropped despite the fact that an alternative path may exist to the network element.
Traditionally, the problem of stale mappings is addressed by using TARP age timers, which expire stale TARP mappings after a certain interval of time. However, this approach has its disadvantages, as TARP age timer intervals are relatively long which may cause connectivity to be down for a long time. Shortening age timer intervals is often not a viable solution, as shortening timer intervals would increase network traffic.